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Biomedical subjects

L Cristofolini

Publications and source records attributed to L Cristofolini.

42 records · Page 3Linked to original sources
PubMed1995

Influence of thigh muscles on the axial strains in a proximal femur during early stance in gait.

This work is focused on the in vitro simulation of the loads occurring in the femur during early stance in gait, for hip prosthesis stress shielding test purposes. Ten thigh muscles (the three gluteal muscles, the three vasti, rectus femoris, adductor longus and magnus, biceps femoris), simulated by nylon straps, were tested in order to establish their influence on the strains in the proximal femur. Axial and hoop strains were recorded from 16 strain gauges for the effect of each muscle and compared to the strains recorded as a result of the hip joint reaction force only (i.e. without muscle simulation). It appears that the three glutei are the principal muscles in determining the vertical strains, however the rectus femoris, biceps femoris and the adductors were also seen to significantly affect the strain pattern. The inadequacy of increasing the adduction angle and applying the resultant force at the hip joint to simulate the abductors was also confirmed.

Femur↗
PubMed1995

Initial stability of uncemented hip stems: an in-vitro protocol to measure torsional interface motion.

The difficulty in quantitatively assessing the inherent variables of surgical stem insertion and interfemur differences continues to be a problem in experimental methodologies which assess hip stem stability. An in-vitro torsional stability protocol was developed which limited the mechanical testing variability and provided a reproducible micromotion measurement of an uncemented stem in synthetic composite femurs. Using a controlled mechanical stem insertion resulted in less interfemur variability within each group with the coefficient of variation being reduced from 35% overall to less than 20%. Femurs with shallow stem insertion depths had significantly larger micromotion than femurs having deep stem insertion depths. The sensitivity of the experimental protocol and the synthetic composite femurs to the varied functional behaviour of three different stem designs was demonstrated. The stem with a hollowed anterior-to-posterior proximal section experienced significantly more motion than the two stems with full proximal sections, reinforcing the need for proximal contact to ensure minimal micromotion in torsional loading.

Biocompatible Materials↗
PubMed1994

Evaluation of experimental and finite element models of synthetic and cadaveric femora for pre-clinical design-analysis.

The aim of this study was to determine the validity with which the finite element method could model synthetic bone and thereby determine the appropriateness of such femur analogues for application in pre-clinical tests. The performance of these synthetic femora was compared with cadaveric bone when employing the same geometric and material definition protocols. A four-point bend loading configuration was selected for this analysis. Four synthetic femurs and an embalmed cadaveric bone were tested experimentally to determine the structural bending stiffness (k) for the diaphysis of these bones. A finite element (FE) model was generated and an analysis performed for each bone type to estimate the Young's modulus (E) required to obtain a model stiffness equivalent to that obtained experimentally. The estimated material elastic modulus in the FE model for the synthetic femur was found to be very similar to available data for this bone analogue. The estimated cadaveric bone modulus however was found to differ significantly from documented values for cortical bone. A theoretical analysis demonstrated the great sensitivity of the estimated modulus value to the accuracy of the geometric definition. The very low variability found in the experimental test on the synthetic bones together with their more regular geometry and the possibility of achieving greater accuracy in geometric definition was shown to enable the production of a valid FE model of this bone for an isotropic homogeneous material description. Conversely, the greater irregularity of geometry, together with the less obvious differentiation between the cortical and cancellous bone in the cadaveric specimen makes accurate geometric description of this bone very difficult. This fact, together with the uncertainty concerning the quality of the cadaveric bone and its viscoelastic response during mechanical testing, makes reproduction of its behaviour in a FE model a much more demanding task. It is suggested that this greater capability of reproducing the experimental behaviour of the synthetic bone makes them a very useful model for both experimental and numerical studies which involve in-vitro pre-clinical testing of implant design and stem-bone behaviour.

Artificial Organs↗